Microscopic polyangiitis (MPA) is a form of vasculitis—a family of rare disorders characterized by inflammation of the blood vessels, which can restrict blood flow and damage vital organs and tissues. MPA most commonly affects the small- to medium-sized blood vessels, particularly involving the kidneys, lungs, nerves, skin, and joints. MPA can worsen rapidly, so early diagnosis and treatment are essential to prevent kidney or respiratory damage, or organ failure.
MPA is known as an ANCA-associated vasculitis, referring to a blood protein (anti-neutrophil cytoplasmic antibody) that attacks the body’s own cells and tissues. Other forms of ANCA-associated vasculitis include eosinophilic granulomatosis with polyangiitis (EGPA) and granulomatosis with polyangiitis (GPA). People with these types of vasculitis often test positive for ANCA, although the test is not conclusive.
MPA is a serious but treatable disease. The traditional course of treatment includes corticosteroids such as prednisone used in combination with other medications that suppress the immune system and reduce inflammation. Even with treatment, MPA is a chronic condition with periods of relapse and remission, so ongoing medical care and monitoring are necessary.
The cause of MPA is not yet fully understood by researchers. Vasculitis is classified as an autoimmune disorder, a disease which occurs when the body’s natural defense system mistakenly attacks healthy tissues. Researchers believe an infection may set the inflammatory process in motion in MPA. Environmental and some genetic factors may also play a role in vasculitis.
MPA can affect people of all ages, but the average age of onset is approximately 50. It affects both men and women, but men may get MPA more often. The disease is more frequent among Caucasians but can affect people of any race or ethnic background.
MPA is rare, with prevalence estimated at 1 to 3 cases per 100,000 people in the United States. Internationally, the incidence is approximately 2 cases per 100,000 people in the United Kingdom and an estimated 1 case per 100,000 people in Sweden.
The symptoms of MPA and their severity can vary greatly from person to person, depending on which blood vessels and organs are affected. For some the disease is mild, while for others it may be severe, or even potentially life-threatening if untreated. MPA symptoms may come on slowly over a period of months, or develop rapidly in a matter of days.
People with MPA often feel generally ill, with flu-like symptoms of fatigue, fever, loss of appetite and weight loss. Other symptoms may be related to organ systems affected.
- Kidney inflammation, which may be associated with bloody or dark urine. (Note: A patient can have kidney disease without having symptoms; therefore, patients with vasculitis should have regular urine tests.)
- Skin rashes/lesions, especially on the legs
- Cough (coughing up blood, shortness of breath)
- Nerve problems (tingling, numbness, pain, weakness, “foot drop” or “wrist drop”—inability to lift your foot or wrist)
- Joint and muscle pain
- Abdominal pain with eating
- Eye irritation
Serious, even life-threatening complications, can occur with MPA, especially with the kidneys and lungs. If you have symptoms that don’t go away, have bloody or dark urine, or are coughing up blood, contact your doctor right away.
Because there is no single test for diagnosing MPA, your doctor will consider a number of factors, including a thorough medical history, physical exam findings, and results of laboratory tests and imaging studies. A biopsy of the affected tissue is usually obtained to confirm the diagnosis.
- Urinalysis: The presence of red blood cells may indicate kidney inflammation. Your doctor may use this test to help diagnosis MPA, and to monitor the kidneys during and after treatment.
- Blood tests: The ANCA test can be helpful when positive. Blood tests that can detect inflammation include the erythrocyte sedimentation rate (ESR) test, commonly called the “sed rate,” and the C-reactive protein (CRP) test. All these tests may support a diagnosis of MPA, but are not conclusive on their own. A tissue biopsy is typically needed.
- Tissue biopsy: This surgical procedure removes a small tissue sample from an affected organ, which is examined under a microscope for signs of inflammation or tissue damage. Tissues that might be biopsied for MPA include kidney, lung, skin, nerve and muscle.
- Imaging studies: Chest X-rays may reveal changes in your lungs that are characteristic of MPA. Computed tomography (CT) and magnetic resonance imaging (MRI) scans provide more detailed images of your internal organs and can show abnormalities.
Treatment is based on a number of factors, including disease severity and organ involvement. The cornerstone of treatment for MPA is corticosteroids such as prednisone used in combination with other medications that suppress the immune system and reduce inflammation.
For severe disease, the biologic drug rituximab (Rituxin) may be used in combination with prednisone. The U.S. Food and Drug Administration (FDA) in 2011 approved rituximab for the treatment of MPA and GPA. (Biologic medications are complex proteins derived from living organisms. They target certain parts of the immune system to control inflammation.)
In October 2021 the U.S. Food and Drug Administration approved avacopan (TAVNEOS) as an adjunctive treatment of adult patients with severe active ANCA-associated vasculitis, and specifically for GPA and MPA. Results from ADVOCATE, the pivotal Phase III study evaluating avacopan, were published in The New England Journal of Medicine earlier this year.
Another option for severe disease is cyclophosphamide, a chemotherapy-type drug that blocks abnormal growth of certain cells in the body, in combination with prednisone. Prednisone is typically started at a high dose and then tapered off slowly. Cyclophosphamide can lower the body’s ability to fight infection, so it is usually limited to a three- to six-month period and replaced with less toxic medications such as mycophenolate mofetil and azathioprine, or methotrexate, a drug commonly used to treat rheumatoid arthritis. Milder forms of MPA are typically treated with a combination of prednisone and methotrexate.
Some individuals may experience kidney failure, a serious complication that requires dialysis and/or a kidney transplant. Another option for those with very serious MPA affecting the kidneys or lungs is “plasmapheresis.” Plasmapheresis is a dialysis-like procedure that clears proteins from the plasma of the blood and replaces it with plasma from a donor, or with a plasma substitute.
Once in remission, most patients will likely need to continue taking maintenance medications, such as azathioprine, methotrexate or rituximab, to keep the disease under control. The dose of steroids is usually tapered during remission.
The medications used to treat MPA have potentially serious side effects, such as lowering your body’s ability to fight infection, and potential bone loss (osteoporosis), among others. Therefore, it’s important to see your doctor for regular checkups. Medications may be prescribed to offset side effects. Infection prevention is also very important. Talk to your doctor about getting a flu shot, pneumonia vaccination, and/or shingles vaccination, which can reduce your risk of infection.
Even with effective treatment, MPA is a chronic disease, and relapses may occur. If your initial symptoms return or you develop new ones, report them to your doctor as soon as possible. Regular doctor visits and ongoing monitoring of lab and imaging tests are important in detecting relapses early.
Effective treatment of MPA may require the coordinated efforts and ongoing care of a team of medical providers and specialists. In addition to a primary care provider, you may need to see the following specialists: rheumatologist (joints, muscles, immune system); pulmonologist (lungs); nephrologist (kidneys); dermatologist (skin); neurologist (brain/nervous system); or others as needed.
The best way to manage your disease is to actively partner with your health care providers. Get to know the members of your health care team. It may be helpful to keep a health care journal to track medications, symptoms, test results and notes from doctor appointments in one place. To get the most out of your doctor visits, make a list of questions beforehand and bring along a supportive friend or family member to provide a second set of ears and take notes.
Remember, it’s up to you to be your own advocate. If you have concerns with your treatment plan, speak up. Your doctor may be able to adjust your dosage or offer different treatment options. It is always your right to seek a second opinion.
Living with a chronic disease such as MPA can be challenging at times. Fatigue, pain, emotional stress, and medication side effects can take a toll on your sense of well-being, affecting relationships, work and other aspects of your daily life. Sharing your experience with family and friends, connecting with others through a support group, or talking with a mental health professional can help.
There is no cure for MPA at this time, but with early diagnosis and proper treatment, many patients can lead full, productive lives. Because relapses can occur with MPA, follow-up medical care is essential.
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